Regulation of nitrogen fixation in Azorhizobium caulinodans: identification of a fixK‐like gene, a positive regulator of nifA

Kaminski, P.A.; Mandon, Karine; Arigoni, Fabrizio; Desnoues, Nicole; Elmerich, Claudine

doi:10.1111/j.1365-2958.1991.tb00820.x

Cited by 56 publications

(49 citation statements)

References 31 publications

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“…Strain JRG1728, harboring pRJ9020, showed very low, FixK-dependent expression of the lacZ fusion under aerobic conditions, whereas anaerobically this expression was enhanced sixfold ( (Fig. 2) (3,24). (ii) It shares the strongest overall amino acid sequence similarity with the rhizobial FixK proteins, especially with the one of R. meliloti.…”

Section: T V P L P M S R Q D I a D Y L G L T I E T V S R T F T K L mentioning

confidence: 99%

Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

1992

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We describe the cloning, sequencing, regulation, and mutational analysis of a Bradyrhizobium japonicum fixK-like gene whose product belongs to the family of Fnr-Crp-related regulatory proteins. The predicted 237-amino-acid FixK protein was found to share between 28 and 38% sequence identity with the Escherichia coli Fnr protein, other bacterial Fnr-like proteins (FnrN, Anr, and HlyX), and two rhizobial FixK proteins.

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Section: T V P L P M S R Q D I a D Y L G L T I E T V S R T F T K L mentioning

confidence: 99%

Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

1992

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“…Nitrogenase assays of bacteria in the freeliving state and in planta were performed as reported previously (13,15). ␤-Galactosidase assays of bacteria in the free-living state were performed principally as described previously (24). Precultures in the stationary phase were used to inoculate rich medium.…”

Section: Methodsmentioning

confidence: 99%

Characterization of Azorhizobium caulinodans glnB and glnA genes: involvement of the P(II) protein in symbiotic nitrogen fixation

et al. 1997

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The nucleotide sequence and transcriptional organization of Azorhizobium caulinodans ORS571 glnA, the structural gene for glutamine synthetase (GS), and glnB, the structural gene for the P II protein, have been determined. glnB and glnA are organized as a single operon transcribed from the same start site, under conditions of both nitrogen limitation and nitrogen excess. This start site may be used by two different promoters since the expression of a glnB-lacZ fusion was high in the presence of ammonia and enhanced under conditions of nitrogen limitation in the wild-type strain. The increase was not observed in rpoN or ntrC mutants. In addition, this fusion was overexpressed under both growth conditions, in the glnB mutant strain, suggesting that P II negatively regulates its own expression. A DNA motif, similar to a 54 -dependent promoter consensus, was found in the 5 nontranscribed region. Thus, the glnBA operon seems to be transcribed from a 54 -dependent promoter that operates under conditions of nitrogen limitation and from another uncharacterized promoter in the presence of ammonia. Both glnB and glnBA mutant strains derepress their nitrogenase in the free-living state, but only the glnBA mutant, auxotrophic for glutamine, does not utilize molecular nitrogen for growth. The level of GS adenylylation is not affected in the glnB mutant as compared to that in the wild type. Under symbiotic conditions, the glnB and glnBA mutant strains induced Fix ؊ nodules on Sesbania rostrata roots. P II is the first example in A. caulinodans of a protein required for symbiotic nitrogen fixation but dispensable in bacteria growing in the free-living state.Azorhizobium caulinodans ORS571, isolated from stem nodules of its host plant, the tropical legume Sesbania rostrata, fixes nitrogen both during symbiosis and in the free-living state (15). In the free-living state, this strain assimilates fixed ammonium for growth, via the glutamine synthetase (GS)/glutamate synthetase pathway (14). During symbiosis, ammonium produced by nitrogen fixation is exported from the bacteroid to the vegetal cell, where it is assimilated by the plant GS. As in enteric bacteria, only one GS (GSI) has been characterized in A. caulinodans (14), whereas two forms (GSI and GSII) have been identified in most rhizobia (9). In enteric bacteria and rhizobia, GS activity is modulated by reversible adenylylation in response to changes in the intracellular glutamine/2-ketoglutarate ratio, reflecting the level of cellular nitrogen (20). In Escherichia coli, under conditions of nitrogen limitation, the P II protein, encoded by glnB, is uridylylated by the glnD gene product. Under conditions of nitrogen excess, P II is deuridylylated and activates an adenylyltransferase (28). This enzyme transfers an AMP group to a tyrosine residue in each of the 12 subunits of the GS; the fully adenylylated form of the enzyme is less active (33). The structural gene for GS (glnA) is part of the glnALG operon, where glnL and glnG (also designated ntrB and ntrC) are the structura...

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“…In both cases, the two component regulatory proteins FixL and FixJ induce fixK transcription under oxygen-limiting conditions. However, the Fnr-like protein FixK in A. caulinodans positively controls nifA, whereas in R. meliloti, it is a negative regulator of nifA and a positive regulator of fixN (2,21).…”

mentioning

confidence: 99%

“…It is able to grow in the free-living state at the expense of dinitrogen and also to fix nitrogen symbiotically in the stem and root nodules of the tropical legume Sesbania rostrata (9)(10)(11). A model of the regulation of nifandfix gene expression in A. caulinodans has been proposed (20,21,35,46). Transcription of nifA is controlled by both oxygen and ammonia via the fixLJ, fixK, and ntrBClntrYX gene products.…”

mentioning

confidence: 99%

Functional analysis of the fixNOQP region of Azorhizobium caulinodans

1994

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The deduced amino acid sequences of four open reading frames identified upstream of thefixGHI region in Azorhizobium caulinodans are very similar to the putative terminal oxidase complex coded by the fixNOQP operons from Rhizobium meliloti and Bradyrhizobium japonicum. The expression of the A. caulinodansfixNOQP genes, which was maximal under microaerobiosis, was positively regulated by FixK and independent of NifA. In contrast to the Fix-phenotype of B.japonicum and R. melilotifixN mutants, anA. caulinodansfixNO-deleted mutant strain retained 50%o of the nitrogenase activity of the wild type in the symbiotic state. In addition, the nitrogenase activity was scarcely reduced under free-living conditions. Analysis of membrane fractions of A.caulinodans wild-type and mutant strains suggests that the fixNOQP region encodes two proteins with covalently bound hemes, tentatively assigned tofixO andfixP. Spectral analysis showed a large decrease in the c-type cytochrome content of thefixN mutant compared with the wild type. These results provide evidence for the involvement of FixNOQP proteins in a respiratory process. The partial impairment in nitrogen fixation of thefixN mutant in planta may be due to the activity of an alternative terminal oxidase compensating for the loss of the oxidase complex encoded byfixNOQP.

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Regulation of nitrogen fixation in Azorhizobium caulinodans: identification of a fixK‐like gene, a positive regulator of nifA

Cited by 56 publications

References 31 publications

Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

Characterization of a fixLJ-regulated Bradyrhizobium japonicum gene sharing similarity with the Escherichia coli fnr and Rhizobium meliloti fixK genes

Characterization of Azorhizobium caulinodans glnB and glnA genes: involvement of the P(II) protein in symbiotic nitrogen fixation

Functional analysis of the fixNOQP region of Azorhizobium caulinodans

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